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• Anyone who has received a herpes diagnosis may be twice as likely to develop dementia than people who have not, according to a new study from Uppsala University in Sweden.
• HSV-1, the type of the virus that causes cold sores or oral herpes, is most associated with the risk of dementia.
• Nearly 80% of the adult population in Sweden and 57% to 80% of adults in the United States carries that type.

Anyone who has received a herpes diagnosis may be twice as likely to develop dementia than people who have not, according to a new study from Uppsala University in Sweden.

The study, which was published in the Journal of Alzheimer’s Disease, followed 1,000 70-year-old subjects for 15 years and confirmed previous research about the associations with the herpes virus and dementia.

Herpes results from infection with the herpes simplex virus (HSV), of which there are two types. Herpes simplex virus type 1 (HSV-1) causes oral herpes, affecting the mouth and surrounding skin but also potentially the genital region. Herpes simplex virus type 2 (HSV-2) typically causes genital herpes and is usually sexually transmitted. Nearly 572,000 people have HSV-2 infections each year, according to the Centers for Disease Control and Prevention (CDC).

Dementia is a wide term for cognitive decline disorders like Alzheimer’s disease and vascular dementia. It is associated with aging but is not a usual part of getting older.

Erika Vestin, a lead author of the study and a Ph.D. student at Uppsala University, told Medical News Today that the research confirms prior knowledge about the connections between dementia and herpes, but causality is still not concrete.

“We still do not have answers regarding causal mechanisms of this association, whether the virus causes the disease or if there is an indirect link,” Vestin said.

“Further, the association remains to be studied in different social and ethnic groups, and potential effects of herpes drugs on dementia risk need to be investigated in pharmaceutical drug studies,” she added.

How common is herpes and dementia?

According to the World Health Organization (WHO), more than 55 million people worldwide have dementia and nearly 10 million more will receive a diagnosis of dementia each year. By 2030, it is estimated that the number of people with dementia will reach 78 million.

HSV, which remains for a person throughout their life, is quite common. According to the WHO, around 67% of people under age 50 globally have an HSV-1 infection, and 13% under age 50 have an HSV-2 infection., and 13% under age 50 have an HSV-2 infection. Most people with HSV-2 may not know they have it: Approximately 87.4% of people between the ages of 14 and 49 with genital herpes do not have a clinical diagnosis.

Up to 80% of the adult population in Sweden may have contracted HSV-1 at some point. The statistics are similar in the United States: 57% to 80% of adults here have oral herpes.

The herpes virus causes sores or blisters in or around the mouth or genitals, alongside other symptoms. There is no cure for herpes, but treatment can help manage symptoms and reduce the likelihood of outbreaks recurring and transmission to partners.

What is the link between herpes and dementia?

Vestin said that the oral form of herpes is most likely the main factor in any connection between HSV and dementia, but that the virus itself can complicate those connections.

“The main culprit seems to be HSV-1, which commonly infects the oral region,” Vestin said. “However, HSV-1 and HSV-2 can both infect either the oral or the genital region, which is important to have in mind when these studies are conducted.”

Dr. Monica Gandhi, MPH, an infectious diseases specialist with the University of California, San Francisco, told MNT that the study does not prove causality.

“There could be important differences between those with or without herpes simplex virus (HSV) IgG status (past exposure) and those who developed dementia or not. It is difficult to control all confounders that have been traditionally associated with dementia (like diabetes, hypertension, history of stroke or myocardial infarction), and the authors state that their entire cohort had relatively low rates of these conditions,” Dr. Gandhi said.

“The authors did not find an association between treatment for HSV and dementia, which would be an interesting observation to see in another study if we wanted to be more convinced of a causal link,” Dr. Gandhi added.

“A good matched study where a group is matched on almost all possible confounders for dementia (hypertension, diabetes, smoking, other risk factors) to another group with the same risk factors but only one difference (HSV IgG status) could be helpful in providing further evidence,” she added.

Should I be worried if I have a herpes diagnosis?

Vestin suggested that getting diagnosed and treated with widely available drugs for the herpes virus would benefit anyone who does have it and indicated that previous research backs this.

“There are indications from large register studies that herpesvirus drug use may be associated with a decreased risk of dementia among symptomatic herpes simplex carriers. However, there are no pharmaceutical trials to confirm this. For now, herpes simplex carriers will have to rely on the same advice as the rest of the population, involving mainly lifestyle factors and cardiovascular health,” she said.

Dr. Gandhi said that the rates of herpes and dementia are different enough — and there are wildly divergent factors for any individual’s susceptibility — to warrant some caution around the study’s findings.

“The prevalence of HSV-1 and HSV-2 is very high in the population (up to 80%) and the rate of dementia is fortunately much lower. Traditional risk factors for strokes (which can induce dementia) include diabetes, hypertension and smoking, so keeping those factors controlled can be helpful for a person’s individual risk of dementia,” Dr. Gandhi said.

“Given how common herpes virus infection is [in] young people, I would not let this study concern you too much,” she added.